This study will examine the role of aromatase in the formation and storage of auditory song memories in the zebra finch caudomedial nidopallium (NCM). The NCM is postulated to play a role in song discrimination and in the formation of auditory memories. In songbirds, the caudal domain of NCM is defined by the expression of estrogen synthesizing aromatase, suggesting that the NCM consists of 2 domains, 1 rostral and 1 caudal, whose function is likely to be influenced by locally synthesized estrogen. The goal of the proposed study is to identify whether rostral and caudal NCM constitute molecularly, structural, and functionally distinct domains, and to determine whether aromatase expressed in the caudal NCM influences the formation of auditory song memories. This study will contribute to our understanding of the role that estrogens synthesized in the brain play in long-term memory formation, and allow us to understand the molecular, structural, and functional organization of the NCM in birds. In Aim 1, we will determine whether the rostral and caudal domains of NCM differ in their molecular, structural, and functional organization. We will first identify whether rostral-to-caudal differences in NCM response properties correspond to differences in the expression of a song-regulated gene, zenk. Microarray studies will then be used to identify novel genes that are song-evoked and differentially expressed across rostral and caudal NCM. Anatomical tract-tracing studies will be used to identify features of domain-specific connectivity. In Aim 2, we will determine whether aromatase expressed in the NCM is involved in the storage of auditory memories. The role of estrogen in an auditory processing task will be investigated by measuring the effects of an aromatase inhibitor on the song-specific induction of auditory-evoked zenk.